Tubular liners for sewer rehabilitation have been known for a long time. Here, for example, glass fiber tubular liner systems with UV or steam curing are known, in which the pipe to be rehabilitated must introduce a thick-walled film made of PE with a high density (HDPE—high density polyethylene), which—in most cases in the cross-sectional shape of a semicircle—is applied on the inner wall of the pipe. Subsequently, a flexible insert tube (also called a “tubular liner” or simply a “liner”) is drawn into the pipe to be rehabilitated (drawing-in process), whereas the insert tube slides over the sliding film. On the one hand, this prevents damage to the insert tube through the inner pipe wall or objects in the pipe; and on the other hand, the friction between the insert tube and sliding film is very low and facilitates the drawing in of the insert tube. Its functioning is similar to that of a shoehorn. With glass fiber tubular liner systems with UV or steam curing, such an insert tube (tubular liner) usually features an inner and an outer tube, between which a carrier material (for example, glass fibers), which is impregnated with reactive plastic resin, is introduced. For example, commercially available UP resins (polyester or unsaturated polyester resins), VE resins (vinyl ester resins) or EP resins (epoxy resins) are used as the reactive plastic resin. With UP or VE resins, the curing of the resins takes place, for example, with the aid of photoinitiators. However, curing may also take place thermally. The insert tube remains inflated in the pipe until it makes contact with the inner pipe wall or sliding film, in order to subsequently cure the resin—for example, with the aid of UV radiation from a UV radiation source slowly drawn out through the pipe. Finally, the inner film of the insert tube can be drawn out and removed. The layer with the carrier material is then exposed to the substances to be led through the pipe.
A tubular liner is known, for example, from WO 2012/159702. Thereby, for the combination of inner tubular film, resin-carrier layer and outer tubular film, a protective tube made of a tear-resistant material in the form of a truck tarpaulin material (that is, PVC-reinforced fabric) is arranged, which features a connecting section extending in the longitudinal direction of the tubular liner, which can be elongated by introducing compressed air into the tubular liner in the circumferential direction. With one embodiment, the protective tube made of tear-resistant, non-stretchable material features such a width that, upon the wrapping around of the outer tubular film, the two longitudinal edges do not abut each other or overlap. In order to bridge the gap (viewed in cross-section) that thus emerges between the longitudinal edges of the protective tube, a connecting film piece made of a stretchable material is provided, which is connected to such longitudinal edges of the protective tube. The premature curing of the resin is prevented by the fact the outer, mechanically fragile tubular film is formed in a manner impermeable for UV radiation, as is known from the state of the art.